Method of igniting rocket fuels



1963 J. T. HAMRICK ETAL 3,101,589

METHOD OF IGNITING ROCKET FUELS Filed'Nov. 10, 1958 .[ZYVEZTZUFE dose :6 7. fiam/v'cw Les/1? C. lease gas generator and structure related thereto.

United States Patent 3,101,589 METHOD OF IGNITING ROCKET FUELS Joseph T. Hamrick, Roanoke, andLeslie C. Rose, Rocky Mount, Va., assignors to Thompson Ramo Wooldridge Inc., Cleveland, Ohio, a corporation of Ohio Filed Nov. 10, 1958, Ser. Nb. 772,787 3 Claims. (Cl. fill-35.4)

The present invention relates broadly to the decomposition of fuels especially suitable for rocket propulsion, and is more particularly concerned with a new and improved method of initiating exothermic decomposition of hydrazine type fuels featuring the use of solid oxidizing agents.

It is a of the present invention to provide a method of spontaneously igniting fuel compositions by use of oxidizing agents hyper-golic therewith.

Another object of this invention lies in the provision of a starting method for hydrazine type fuels which. features as an essential step thereof the injection of the fuel into an essentially closed chamber into contact with a solid oxidizer positioned therein.

Another object of this invention is to provide a proce dure for starting gas generators which comprises admitting therein hydrazine fuel and eifecting contact between said fuel and a solid oxidizer contained in said gas generator to spontaneously ignite the hydrazine fuel and initiate exothermic decomposition thereof with release of substantial [gas pressures firom the generator.

A further object of the invention lies in the provision of an improved igniting method for hydrazine type fiuels,

featuring the combination therewith of a solid oxidizer selected from the group consisting essentially of lead dioxide, potassium permanganate, calciumhypochlorite,

pentox-ide and sodium lowing description, particularly when talken in connection with the accompanying drawings.

cfectiveness in initiating a spontaneous decomposition of hydrazine employing either potassium permanganate or iodine pentoxide as the oxidizing agent. ,The generator comprises a hollow generally cylindrical main body portion 11=and an integral, hollow reduced diameter tail pipe portion 12 providing at one end an exhaust nozzle 13. The main body portion 11 receives at one end a threaded cap member .14 having at generally its radial center a fuel line connection 15 communicating interiorly of the main body portion with a fuel injector nozzle 16. It is to be seen that the fuel line connection and injector nozzle are in general axial alignment with one another;

The main body portion 11 of the generator 10 provides interiorly thereof a reaction chamber 17 and Welded or otherwise secured to the walls of the chamber 17 is a retainer plate 18 suitably. :apertured' and providing a mounting surface for a plurality of metal coilsglQ which function as a catalyst and to stablize the flame front of In the drawings, wherein like numerals are employed to designate like parts throughout the same:

FIGUREI is a fragmentary perspective view of one form of gas generator which may be employed in the practice of the method of this invention; and

FIGURE 2 is a iragmentary perspective view of a diftferent form of gas generator effective in performance of the novel steps herein disclosed.

Applicants invention lies in the discovery that fuel instantaneous development of pressures by combining with the iuel an oxidizing agent selected from the group consisting of lead dioxide, potassium permanganate,

calcium hypochlorite, molyb dic acid, tungstic acid, iodine pentoxide and sodium chlorite. The utilization of solid oxidizers in accordance iwth this invention produces in all cases smooth starts, and the emission of combustion products having no marleed deleterious efiects upon the Substantial investigations have demonstrated that the starts using solid oxidizers proceed extremely rapidly and are essentially instantaneous, only requiring on the order of about onefifth to twofifths of a second to reach maximum pressures. While reaction chambers. of various structural characteristics may be employed in the practice of the present method, there is illustrated in FIGURES l and 2 particular gas generators employed by applicants to elfect instantaneous starts of hydrazine compounds.

Referring now to FIGURE 1, there is shown a gas generally designated by the numeral 10 and of proven efthe decomposition reaction. A material found suitable tor the coil springs 19' is 304 stainless steel.

While the solid oxidizer may be mounted interiorly of the generator body portion 11 in various ways, particularly good results have been obtained with the support arrangement of FIGURE 1. arrangement comprises a generally cylindrical shell member 20- at one end of which is Welded orotherwise secured a relatively heavy wire screen 211. Carried ppon the screen 21 is a screen 22 of relatively liner mesh, and between said screen. 22 and an identical screen member 23 is a quantity of the selected,

oxidizer 24. 1 0 complete the oxidizer \supportarrangement there is preferably superimposed upon the screen 23 a relatively heavy mesh screen2'5, which may correspond to the bottom screen 21, and it'is tobe seen irom FIGURE 1 that the screen assembly and oxidizer are held firmly in place by. means of retaining ring or the like 2-6. which is snapped into proper position. The shell 20,screens 2'1, 22, 23 and 25, and the ing although the basket 27 could of course be supported in other ways. I

At the end of the main body portion ll adjacent the tail pipe portion 12 there is arranged a pressure tap con nection 29 by means of which pressure readings are obtained, and downstream thereof is thermocouple 30 to provide the desired temperature information. Other pressure and temperature connections may be made at other locations along the gas generator 10 when desired.

A series of runs have been madeutilizing the gas generator 10 of FIGURE 1 supporting in the reaction chamber 17 thereof potassium permanganate or iodine pentoxide. The. results obtained from these tests employing anhydrous hydrazine as the fuel are set forth in theillu'strative examples below. i

EXAMPLE I Twenty grams ofipotassium permanganate in crystalline form was located in the basket 27 between screens 22 and 23 of 200 mesh size. A variable area injector nozzle 16 was employed, andthe exhaust nozzle 13 bad a diameter of 0.239 inch. The net volume of the generator 10 when empty was 530 cc. No external heating means were employed, and the catalyst was 414 grams of .304 stainless steel springs. The weight of the oxidizer basket with oxidizer loaded therein before the start of 3,101,589 Patented Aug. 27, 1963 a the run was-'9 0.6 grams, whileafitercomplet-mn of the I run the-total weight was 77.6 grams. 7

' Anhydrous hydrazine was admitted to the reaction chamber 17 in spray form throughthe fuel line at a pressure of 600-p.sLi. -The run was permitted to continue I for eight minutes-and continuously 'therethrough temperature and pressure readings were obtained;- Tempera- "ll lI6S wS6IlS6Cl-by'ihe'lIh8lIl1OCOl1ple-COlll16Ctl0I1' were recorded on a multipoint Brown recorder, while fuel flow I -rate, fuel supply pressure and reaction chamber pressure was continuously recorded on Sanborn direct writing oscillognaphs. A base flow rate of 0.5 :g.p.m./cm. was

usedQand the base 'rates'of supply and chamber pressures were each 250 p.s.i'./cm. The amount of time required for eachv start was observed from the oscillograph pressure trace of supply pressure, thestarting point of the reaction being shown by asudden drop in supply pressure, and the'time interval required for starting was measured from 'the pressuredrop point to the point at which maximum pressure'wasachieved; In the case potassium permanganate asYthe solid oxidizer, the start was made in onefifth of a second; As noted, continuously throughout the run pressure and temperature information was recorded, and the results obtained during the eight minute run are set-forth inltabular form below.

potassium -per manganate initiated a spontaneous decomi represents the characteristic gas velocity. The formula .einployedto'determineC is i I PA c. tg C I t oat area, g is acceleration of gravity, and W is weight flow of pr ll n :The characteristic length of the reaction chamber 17 v -as employed in thedecomposition of hydrazine utilizing potassium permanganate was 638. Characteristic length is determined fromthe equation' WV L .Ae r

"where? V is chamber volume and A, is exhaust nozzle throat area; The minimum L at which jgood operation can 'be' obtainedvaries greatly with generator design. It

varies with the type of fuel injector nozzle '16, method 'O'f flame front stabilization (coils 19),:shap'e of the reaction ohamber17, and kind ofmaterialused for the internal surfaces thereof. 1

, EXAMPLE II I Tests were also conducted utilizing iodine pentoxide I as the solid oxidizer in initiating spontaneous decomposition of anhydrous'hydrazine. The gas generator 10 of 1 FIGURE 1" was employed, a'gain'usin'g a variable area type injector and an exhaust nozzle hai ing a diameter -of0r239' inch. The catalystwas 42.5 grams of 304 stainless steelsprings, approximately one inch in length and positioned'lasshown-irr FIGURE 1. The calculated characteristic length ofthe reaction chamber 11 in the iodine It'is to be" observed from the foregoing data that Y ,positionof hydrazine, causing attainment of maximum 'Tpressures' in about one-fifth of a second. The table in- 7 lcludes asone column thereof the values of 0*, and this Where is the chamber pressure, A, is the exhaust 14".. pentoxid'e runs was 63 6. Five grams .of iodine pentoxide wereloaded in the basket 27 inthe manner shown, and

hydrazine was admitted to the chamber in the form of a spray at an initial supply pressure of 600 p.s.i.' The running time of the test was three minutes, and readings of temperature and pressure were-taken continuously throughout. The iodine pentoxide was in powder form, and when contacted by the hydrazine spray a smooth start was obtainedand a minor amount of blue vapors issued from the exhaust nozzle 13. It was observed subsequent to the test that the basket 27 andscreens therein were in good condition. A minor pressure spike was noted, and

the-pressures and temperatures'observed aregset forth in tabular form below.

' Table 2' Read. Fuel Fuel Oham- Supply Read. time rate rate ber press. Calc.' Temp. No. (min) (lb/hr.) (g.p.m.) press. (p.s .i. 0* F.)

' V, (p.s.i.)

5/25 sec..- 'Press. Spike 7/25 sec." 8/25 sec..- 1 Min 500 99 2 Min 500 99 3Min 495 98 As in the test of the first example, pressure traces of pressures sensed from the tap 29 by strain gauge transducers were continuouslyv recorded on Sanborn direct 'writing oscillographs, employing as a base flow 0.5 g.p.m./cm., a supply pressurebase of 250 p.s.i./cm. and

' a pressure chamber base of 250 psi/cm. The pressure trace of supply pressure was carefully observed and the time interval between the pressure drop and the point' at'which maximum pressure was achieved noted. The time interval with iodine pentoxide was approximately one fifth of a second, approximately the same starting time 'forsporitaneous decomposition as with potassium permanganate. 'It is thus to be seen that ignition of the hydrazine with both potassium permanganate and iodine pentoxide occurs essentially instantaneously with the initiation of exothermic decomposition of the hydrazine and development of maximum. pressures in time intervals not exceeding about one-fifth ofa second.- This is of course markedly less than the starting time required for a mono-propellant start utilizing external heating means or 'a squib starter. In addition, with each of the solid oxi- -dizers herein disclosed a smooth start is obtained, and

accordingly there is avoided the likelihood of violent re- "actions occasionally associated with the use of red fuming nitric acid for bi-propellant star-ts.

An alternate form of gas generator is shown in FIG- URE 2, and this construction has proven particularly effective when utilizing lead dioxide as the solid oxidizer for spontaneous decomposition of anhydrous hydrazine. -'Ilhe exemplary form of gas generator designated as 31 in FIGURE 'Z'comprises a hollow, generally cylindrical main bodysportion or housing 32 having a reduced diametcr generally cylindrical passaged tail'pipeportion 33 carrying an exhaust nozzle at the end thereof. A cap assembly 3'5 'isthreadably received in the opposite end of the housing'32, and said assembly is provided with a fuel.

injector'n'ozzle'36 which is preferably of the variable area type; The cap'assem bly 35 is of course suitably pass/aged to provide communicationwith a reaction chamber 37 interiorly of'the main body portion 32.

-' 'Within thereaction chamber 37 there is located an apertured retainer plate 38'supporting a plurality of coil "springs 39'performing a catalytic action and stabilizing "the flame front produced by reaction of the fuel and solid oxidizer within said reaction chamber. 'The coil springs Y are preferably of 304 stainless steel, and a particular quantity thereof are packed within the reaction chamber in the manner mownyin the drawing. Pressure tap and thermocouple connections '40 and 41 of the character earlier described are employed, and an additional number of said connections may be utilized at other locations along the gas generator to record information at said locations.

The supporting arrangement for the oxidizer in the generator of FIGURE 2 is to be seen as'different from that of FIGURE l. Lead dioxide or other solid oxidizer 42 is contained in a plurality of capsules 43* of generally cylindrical shape formed of wire screen 44, each cylindrical screen being wrapped with coils 45 of stainless steel wire. The wire screen may be of a mesh corresponding to 96 openings per inch utilizing 0.0035 inch diameter 304 stainless steel wire. The Wire coils '45 are preferably formed from 0.040 inch diameter 304 stainless steel wire shaped ona 5 inch rod at eight threads to the inch. While variations may be practiced, the capsules 43 in tests performed to date have been about 1% inches long and approximately inch in diameter. The capsules 43 with oxidizer 42 contained therein may be packed tightly within the reaction chamber 37 in approximately the position shown in FIGURE 2, or if desired the capsules may be supported by a retainer plate 46, apertnred as shown and corresponding generally to the retainer plate 38. The capsules 43 may also be suspended from the cap assembly 35, and mounted in the reaction chamber 37 in various other Ways. As earlier noted, the gas generator '31 is of proven effectiveness with solid oxidizers such as lead dioxide, and the results obtained will now be described in connection with the example following.

EXAMPLE III Fifty coil springs 39 having a total weight of 534 grams and formed of 304 stainless steel Wound on a A inch rod twenty-four threads to the inch and each 3% inches long were located in the reaction chamber -37 in the manner shown in FIGURE 2. Fifty-eight grams of lead dioxide contained in capsules 43 were then inserted in the reaction chamber as illustrated. The gas genenator had a net volume of 25 19 cubic inches, at variable area injector nozzle 36 was used, and the exhaust nozzle 34 had a diameter of 0.239 inch. The characteristic length L* of the reaction chamber was 56 2. The weight of the gas generator 31 when empty was 5672 grams.

Hydrazine was admitted to the gas generator 31 through the injector nozzle 36 at a supply pressure of 300 psi, and during a running time of eighteen minutes observations were continuously made of flow rates, pressures and temperatures. It was observed that initially a substantial quantity of smoke was expelled from the generator, although the lead dioxide provided a very smooth start with anhydrous hydrazine as admitted in spray form. It was noted that the tail pipe 3 3 initially turned a red color, and a reddening of the housing 32 immediately upstream of the tail pipe 33 was seen. The smoke cleared in approximately one-half minute, and some sparking from the tail pipe 33 was seen during the first stages of the run. The fuel flow, pressure and temperature readings as recorded are reproduced in tabular form below.

Table 3 Read. Cham- Supply Read. time Fuel rate Fuel rate her press Cale. Temp. No. (min) (lb/hr.) (g.p.m.) press. (p.s.t.) F.)

1 Peak Press. at start 205 2 Immed ately following Peak 170 3 1 178 36 140 304 4, 100 1, 788 2% 178 36 140 301 4, 100 1, 799 4 177 355 137 300 4,000 1, 779 5 177 355 135 300 4, 000 1, 760 7 175 351 133 299 4,000 1, 747 8% 178 36 133 300 3, 900 1, 740 10 178 36 133 300 3, 900 1,740 11% 178 36 135 300 3, 900 1, 735 3 180 .362 133 300 3, 800 1, 726 14% 180 .362 132 300 3, 800 l, 722 16 180 .363 133 300 3, 800 1, 715 17% 181 364 133 300 3, 800 1, 710

Pressure traces were made in the manner of the earlier disclosed examples, utilizing as the basis for fuel flow, supply pressure and chamber pressure 0.2 g.p.m./cm., p.s.i./em., and 100 p.s.i./crn., respectively. The oscililograph readings on supply pressure were particularly noted to observe the pressure drop occurring as the starting point of the ignition of hydrazine by lead dioxide, and the time interval between the pressure drop and the point at which pressure was reached was slightly less than two-fifths of a second. While the starting time with lead dioxide is relatively greater than with potassium permanganate and iodine pentoxide, all starting times are substantially less than those which are 0 tained with external heat means, starting squi-bs and the like. Further, as earlier stated, red fuming nitric acid has the characteristic of from time to time producing violent reactions, as contrasted with the smooth starts obtained from the solid oxidizers of this invention, and there is presented handling problems with the nitric acid compound.

The foregoing described investigations have been directed to the spontaneous decomposition of hydrazine; however, equally successful results are obtained with unsymmetrical dimethyl hydrazine, as well as with mixtures of hydrazine and unsymmetrical dimethyl hydrazine, as.

for example, a mixture consisting essentially of 5 to 25% by weight of unsymmetrical dimethyl hydrazine in hydrazine. In addition, the fuel employed may consist of a mixture of from 5 to 50% of ammonium nitrate in hydrazine. Further, while there is not set forth in tabular form pressure and starting time information with respect to calcium hypochlorite, molybdio acid and tungstic acid, these materials have been subjected to hypergolic reactivity tests in which hydrazine Was injected onto the surfaces areas of these materials. In all cases, hypengolic reactivity was evidenced, and accordingly the named compounds are effective to initiate decomposition of hydrazine. Other variations and modifications may of course be effected in the compositions and procedures herein disclosed without departing from the novel concepts of the present invention.

We claim as our invention: 1. A method of initiating decomposition of fuel which comprises:

locating in a reaction chamber an oxidizing agent selected from the group consisting of lead dioxide, potassium permanganate, calcium hypochlorite, molybdic acid, tungstic acid, iodine pentoxide, and sodium chlorite, and directing into said reaction chamber and in impinging contact with said oxidizing agent a fuel hypergolic with said oxidizing agent, said fuel being selected from the group consisting of hydrazine and unsymmetrical dimethyl hydrazine. 2. A method of spontaneously igniting and decomposing a fuel which'coniprises:

introducing the fuel into a reaction chamber in contact with a solid oxidizer, said fuel consisting of hydrazine, said oxidizer selected from the group consisting of lead dioxide, potassium permanganate, calcium hypochlorite, molybdic acid, tungstic aoid, iodine pentoxide, and sodium chlorite, and venting from the reaction chamber the exhaust gases produced therein. l 3. A method of imparting propulsive force to missiles which comprises:

locating in the reaction chamber of said missile a solid oxidizer said solid oxidizer selected from the group consisting of lead dioxide, potassium permanganate, calcium hypochlorite, molybdic acid, tungstic acid, iodine pentoxide, and sodium chlorite,

introducing into said chamber in contact with said 7 8 zine, and hydrazine and unsymmetrical dimethyl hy- 2,791,883 Moore et ual. May 14, 1957 drazine, and 2,835,106 Canter May 20, 1958 ventin 'g from the chamber the exhaust gases produced 2,925,709 Mantell e1: a1. Feb. 23, 1960 v 1, ,"therein. 2,932,159 Ter Horst Apr. 12,1960 Q 5 2,988,431 Kresse et a1. June 13, 1961 References C lted 1n the file of 1115 patent OTHER REFERENCES 7 f STATES PATENTS Rockets, May-August 1946, page 7. Copy in 52-5. 2,433,932 stqslck Jam @1948 Au'drieth et al. ,-The Chemistry of Hyrazihe, 1951, pages 2,4 Zwwky et 1948 118 121. (Copy in Scientific Library.)

2,573,471 Malina et a1. Oct. 30; 195 1 10 v 2,772,952 Jacobs Dec. 4, 1956 

1. A METHOD OF INITIATING DECOMPOSITION OF FUEL WHICH COMPRISES: LOCATING IN A REACTION CHAMBER AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF LEAD DIOXIDE, POTASSIUM PERMANGANATE, CALCIUM HYPOCHLORITE, MOLUBDIC ACID, TUNGSTIC ACID, IODINE PENTOXIDE, AND SODIUM CHLORITE, AND DIRECTING INTO SAID REACTION CHAMBER AND IN IMPINGING CONTACT WITH SAID OXIDIZING AGENT A FUEL HYPERGOLIC WITH AID OXIDIZING AGENT, SAID FUEL BEING SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE AND UNSYMMETRICAL DIMETHYL HYDRAZINE. 